Conventionally, a fuel delivery pipe having a plurality of injection nozzles to supply fuel, e.g., gasoline to a plurality of cylinders of an engine has been known. This fuel delivery pipe injects sequentially the fuel introduced from a fuel tank into a plurality of intake pipes or the cylinders of the engine via a plurality of the injection nozzles to mix the fuel with air, thereby burning the air-fuel mixture to generate an engine output power.
Though this fuel delivery pipe is, as described above, for injecting the fuel supplied through an underfloor pipe arrangement from the fuel tank into the intake pipes or the cylinders via the injection nozzles, a fuel delivery pipe as a return type have existed, which belongs to a type having a circuit for returning the surplus fuel to the fuel tank by a pressure regulator in a case of where the fuel is overly supplied into an interior of the fuel delivery pipe. To the contrary to the fuel delivery pipe as the return type, there has been known a fuel delivery pipe as a returnless type having no circuit for returning the supplied fuel to the fuel tank.
Those of the type to return the fuel extra supplied into the fuel delivery pipe to the fuel tank, can always keep the amount of the fuel in the fuel delivery pipe constant, thereby having an advantage such that the pressure pulsation in association with the fuel injection hardly occurs. The fuel supplied to the fuel delivery pipe arranged near the engine cylinder heated at high temperature, however, may be rendered at a high temperature, and the heated surplus fuel is returned to the fuel tank thereby increasing the temperature of gasoline inside the fuel tank. Because it is undesirable that the gasoline vaporizes due to the temperature increase and has negative effects on environment, the fuel delivery pipe as the returnless type has been proposed, which does not return the surplus fuel to the fuel tank.
With this fuel delivery pipe of the returnless type, where the fuel is injected from the injection nozzle into the intake pipes or the cylinders, since there is no pipe for returning the surplus fuel to the fuel tank, pressure fluctuation of the fuel inside the fuel delivery pipe becomes large and causes large pressure waves, so that the pressure pulsation occurs greatly in comparison with the fuel delivery pipe of the return type.
This invention uses the fuel delivery pipe of the returnless pipe having a tendency to easily cause the pressure pulsation. With the conventional arts, if the internal pressure of the fuel delivery pipe is decreased due to the fuel injection from the injection nozzle into the intake pipe or the cylinder of the engine, the pressure wave generated by this rapidly decreased pressure and by the halt of the fuel injection causes the pressure pulsation inside the fuel delivery pipe. After propagated from the fuel delivery pipe and connecting pipes connected to the fuel delivery pipe to the proximity of the fuel tank, the pressure pulsation is returned as reversed from a pressure-regulating valve assembled inside the fuel tank and is further propagated up to the fuel delivery pipe via the connecting pipe. Plural injection nozzles are formed at the fuel delivery pipe and perform injections sequentially to cause the pressure pulsation.
Consequently, the pressure pulsation is propagated as noises in the passenger compartment via clips fastening the under floor pipe arrangement, thereby giving uncomfortable feeing to the driver or passengers.
Conventionally, as a means for suppressing such an adverse effect caused by such a pressure pulsation, a pulsation damper containing a rubber diaphragm is arranged at the fuel delivery pipe of the returnless type for absorbing generated pressure pulsation energy, or the underfloor pipe arrangement arranged under the floor as extending from the fuel delivery pipe to the proximity of the fuel tank is secured under the floor by means of the clips for absorbing vibration, thereby absorbing vibration generated at the underfloor pipe arrangement connecting to the fuel delivery pipe or extending to the tank. These means are comparatively effective enough to suppress the adverse effects caused by occurrences of the pressure pulsation.
However, the pulsation dampers and the vibration absorbing clips are expensive and increase the number of components to result in higher costs while raising a new problem on ensuring an installation space. Therefore, for the purpose of reducing the pressure pulsation without using the pulsation dampers or the clips for absorbing vibration, a fuel delivery pipe having a pulsation absorptive function capable of absorbing the pressure pulsation, have been proposed.
As such a fuel delivery pipes having the pulsation absorptive function, inventions as described in Japanese Patent Application Publication Nos. JA-2000-329030, JA-2000-320422, JA-2000-329031, JA-11-37380, and JA-11-2164 have been known. With these fuel delivery pipes having the absorptive function for the pressure pulsation, a flexible absorbing surface is formed on the outer wall of the fuel delivery pipe, deforming by receiving the occurring pressure in association with the fuel injection, to absorb and reduce the pressure pulsation, thereby to prevent abnormal noise caused by the vibration of the fuel delivery pipe or other components from occurring.
The above described conventional arts, however, have the absorption effects for the pressure pulsation but raise problems such that noises in a high frequency area of more than several kHz are generated outside upon a speaker effect exerted by the absorbing surface.
With the fuel delivery pipe as described in the Japanese Patent Application Publication No. 2000-329030, the inventors of the present invention, and others have proposed making the fuel delivery pipe absorb the pulsation by making an outer wall of the fuel delivery body the flexible absorbing surface. FIG. 46 shows an example where the fuel delivery pipe is made to absorb the pulsation by making a whole of a box shaped cross section of the fuel delivery body 81 of the fuel delivery pipe the flexible absorbing surface. Plural sockets 82 are secured to a bottom surface of the fuel delivery body 81, so the fuel is supplied from a fuel passage 83 into the interior of the injection nozzle, not shown, via a fuel inlet opening 84 of the socket 82. As vertical and horizontal dimensions of the fuel delivery body 81 having the thickness of 1.2 mm made of a carbon steel member, height H and width W can be set to around 32 mm and 20 mm respectively.
The inventors of the present invention, and others assume a situation in which the pressure of ten atmospheres exerts on the interior of the fuel delivery body 81, and make an FEM (Finite Element Matrix) analysis under the condition that a bracket (in reference to FIG. 1) for securing the fuel delivery body 81 and the socket 82 are secured to a bottom surface, thereby calculating an increasing rate of an internal volume while displaying in FIG. 47 the changing situation of the cross section shape with enlarging a variation thereof.
As shown in FIG. 47, a left side wall 85 and a right side wall 86 of an inner wall surface of the fuel delivery body 81 are curved as expanded in a horizontal direction, e.g., from a dashed line to a solid line by receiving an internal pressure, but in terms of an upper wall 87 and a lower wall 88, each of the walls ends up curved as shrunk inwardly, and it was turned out that the increasing rate of the internal volume remains at around 0.55%.
Subsequently, as a result of making the same analysis with transforming the cross section shape in a perpendicular direction to an axis of the fuel delivery body 81, from the box shape into, e.g., a double side concaved shape, a hand drum shape, a flask shape, a reverted flask shape, a trapezoid shape, and a reverted trapezoid shape (in reference to FIG. 1, FIG. 2, FIG. 4 to FIG. 30, and FIG. 37 to FIG. 42), it was found that the increasing rate of the internal volume greatly increases to between 1.1% and 1.8%. It is thought that because lefts and rights of these shapes are originally curved surfaces, curved surfaces are deformed, by receiving the pressure, in a direction to decrease a curvature, and therefore, bending is absorbed in the left and right directions while the upper and the lower surfaces hardly deforms, so that an amount of the internal volume becomes inceased.
Though the FEM analysis is a numerical analysis with use of a computer, a reliability thereof is considerably high because modifications are always made thereto with feedbacks based on a result of reproduced experiments with use of real things.
“A fuel feeding pipe of a fuel injector device for internal combustion engine” according to Japanese Patent Application Publication No. JA-60-240867 discloses that at least one of wall surfaces of a fuel delivery body is elastically structured to attenuate the pulsation of the fuel whereas the cross section of the fuel delivery body is in a triangular shape. The above conventional invention, however, can obtain the attenuation effect of the pressure pulsation but cannot obtain a reduction effect of the noise in the high frequency area.